Liver failure, which can cause death, in most cases is a result of multiple insults. The mechanisms for sensitization to liver injury are not well understood. Pathogen-derived signals recognized by Toll-like receptors can activate both hepatocytes and immune cells in the liver to induced inflammation and sensitization to live injury. Our preliminary data suggest that administration of CpG DNA, a TLR9 ligand, results in granuloma formation and sensitization to a TLR4-lingad-induced liver injury. We postulate that TLR2 activation can amplify TLR9-induced sensitization to subsequent liver injury. We hypothesize that the presence of the common TLR adaptor, MyD88, is critical for granuloma formation and sensitization by TLR9 and TLR2-ligands but also by pathogens such as P. acnes. The Specific Aims of our studies are: 1. To delineate the mechanisms of TLR9-induced granuloma formation and sensitization to subsequent liver injury by a) investigating the role of key cytokines (IFN , IL-12, IL-18) and b) characterizing the inflammatory cell populations involved in granulomas and chemokines (MIP-1?, MCP-1, Mig, IP-10, MDC and TARC ) involved in their recruitment. 2. To investigate the mechanisms of TLR2-mediated amplification of TLR9-induced liver granulomas and sensitization to TLR-induced liver injury by a) testing involvement of adaptor molecules and TLR-mediated downstream signaling in immune cells and in the liver, b) evaluating the role of type I interferons. 3. To determine the role of bone marrow-derived immune cells and liver parenchymal cells in induction of granulomas and sensitization to liver injury and to investigate cross-regulation between these cell populations by testing TLR9-/- or MyD88-/- bone marrow chimeras. Results from these experiments will help to understand molecular pathways that are involved in pathogen-induced sensitization to liver failure. Our results will also help better understand formation of granulomas in the liver that is a common feature of primary biliary cirrhosis and sarcoidosis, diseases with no definitive treatment options at this time. Thus, our study may help to design new therapeutic approaches to prevent liver diseases with granulomas and to attenuate sensitization to liver injury caused by infectious pathogens.